We have continued the study of squirrel monkey calls used in social contexts characterized by quiet affiliative and caregiving behavior. Recent work on the course of vocal development in young squirrel monkeys has been based on our detailed knowledge of the syntactical rules governing adult use of affiliative calls. Because ontogenetic vocal changes in this species promise to be more subtle than obvious, this level of information on adult forms puts us in a good position to study the stages of development leading to the competent, fully socialized adult. We have recorded (using close-in videotaping) the vocal behavior of 6 infants born in our colony during the first 3 months of life, using longitudinal time series sampling. Infant vocal behavior during the first month is very limited, and restricted to simple tonal or pulsed calls associated with nursing. Even at this early stage, however, "aunts" or other female monkeys in the group exhibit great attention to the infant and direct much vocal behavior to it. The role of the infant is largely passive, although some examples of vocal exchanges between infants and aunts have been observed. The significant role of aunts in early socialization and developing vocal competence is a new finding. During FY 88 we completed analysis of vocal recordings collected from adult monkeys after "lights out." These data were collected with Visiting Fellow P. Goedeking, and a joint manuscript based on this project has been submitted for publication. The results support the conclusion that maintaining social contact through vocal signals during the night is of greater benefit to squirrel monkeys than any potential risk from exposure to nighttime predation. Collaborative research on human mother-infant preverbal communication has been largely completed (initial studies of H. and M. Papousek), and several manuscripts are in preparation. Some additional data were added and processed in our computer during FY 88.